Reel-to-reel type tape transport mechanisms, especially those which utilize tape cassettes, are subject to tape fouling. One of the causes of tape fouling, occurs when the tape drive mechanism is initially engaged with the tape and reels. The rotationally driven capstan engages the tape between itself and a biased pinch roller and pulls the tape across the tape head. A take-up reel is also rotationally driven, through a slip clutch, to take-up the slack in the tape after it passes from the capstan. However, at the instant of initial start-up, a loop sometimes develops between the capstan and the take-up reel before the take-up reel has had a chance to remove all the slack in the tape. Depending upon the slackness of the tape, and the lightness of the tape, the loop sometimes has sufficient inertia to instantaneously wrap around the capstan, become caught between the incoming tape and the capstan, and be wound thereon. When this capstan windup occurs, the slip clutch driven take-up reel instantaneously reverses its direction of rotation, due to the tape being drawn therefrom and wound onto the capstan. The windup continues until it is either audibly detected and stopped by the operator or binds up the capstan/pinch roller mechanism.
When detected and stopped, the tape must be carefully unwound from the capstan by hand. However, in some cases, the woundup tape is folded and wrinkled so badly that it must be discarded.
Other causes of loops and potential capstan tape windup have been found to be due to: faulty bearings in the deck take-up reel spindle, causing drag; cassettes that have excessive drag on the take-up reel; tape contaminated with materials such as coffee, jelly and oil; tape formed of very lightweight material; and worn or faulty deck braking mechanisms which fail to maintain a tight take-up reel when the decks are switched between the various drive speeds such as fast forward, forward and fast reverse.
Of course, all the problems involving capstan tape windup and discussed herein equally apply to tape windup that may occur on the pinch roller.
It some cassette tape decks, such as those installed on automotive vehicles the cassettes are inserted through an apertured panel and automatically engaged by the tape deck mechanism for playback. When the tape fully unwinds from its supply reel, except for its attached end, onto the take-up reel, the take-up reel stops rotating. A motion/stop sensing mechanism and circuit causes the tape reel drive mechanism to stop and eject the cassette or reverse the play direction, depending upon the unit.
Except for U.S. Pat. No. 4,348,702, the state of the art motion/stop sensing mechanisms do not distinguish between the proper rotational direction accompanying normal operation and the reverse rotational direction of the take-up reel caused by capstan windup.
The aforementioned patent discloses an embodiment having a set of rotational contacts mounted beneath a tape-up reel spindle platform so as to rotate with the platform and provide an electrical discharge path for a circuit connected to a series of printed circuit board contacts beneath the platform. The set of rotational contacts and take-up reel spindle platform are configured so that a one-way clutch is defined between the contacts and the platform whereby the contacts are only rotated when the platform is rotated in the normal, take-up direction.